(1) Field of the Invention
The present invention relates to a technology for stereoscopic, i.e. three-dimensional (3D), video playback and especially to decoding of the video stream.
(2) Description of the Related Art
In recent years, general interest in 3D video has been increasing. For example, amusement park attractions that incorporate 3D video images are popular. Furthermore, throughout the country, the number of movie theaters showing 3D movies is increasing. Along with this increased interest in 3D video, the development of technology that enables playback of 3D video images in the home has also been progressing. There is demand for this technology to store 3D video content on a portable recording medium, such as an optical disc, while maintaining the 3D video content at high image quality. Furthermore, there is demand for the recording medium to be compatible with a two-dimensional (2D) playback device. That is, it is preferable for a 2D playback device to be able to play back 2D video images and a 3D playback device to be able to play back 3D video images from the same 3D video content recorded on the recording medium. Here, a “2D playback device” refers to a conventional playback device that can only play back monoscopic video images, i.e. 2D video images, whereas a “3D playback device” refers to a playback device that can play back 3D video images. Note that in the present description, a 3D playback device is assumed to be able to also play back conventional 2D video images.
FIG. 100 is a schematic diagram illustrating the technology for ensuring the compatibility of an optical disc storing 3D video content with 2D playback devices (see Patent Literature 1). An optical disc 9201 stores two types of video stream files. One is a 2D/left-view video stream file, and the other is a right-view video stream file. A “2D/left-view video stream” represents a 2D video image to be shown to the left eye of a viewer during 3D playback, i.e. a “left-view”. During 2D playback, this stream constitutes the 2D video image. A “right-view video stream” represents a 2D video image to be shown to the right eye of a viewer during 3D playback, i.e. a “right-view”. The left and right video streams have the same frame rate but different presentation times shifted from each other by half a frame period. For example, when the frame rate of each video stream is 24 frames per second, the frames of the 2/D left-view video stream and the right-view video stream are alternately displayed every 1/48 seconds.
As shown in FIG. 100, the left-view and right-view video streams are divided into a plurality of extents 9202A-C and 9203A-C respectively on the optical disc 9201. Each extent contains at least one group of pictures (GOP), GOPs being read together from the optical disc. Hereinafter, the extents belonging to the 2D/left-view video stream are referred to as “2D/left-view extents”, and the extents belonging to the right-view video stream are referred to as “right-view extents”. The 2D/left-view extents 9202A-C and the right-view extents 9203A-C are alternately arranged on a track 9201A of the optical disc 9201. Each two adjacent extents 9202A-9203A, 9202B-9203B, and 9202C-9203C has the same length of playback time. Such an arrangement of extents is referred to as an interleaved arrangement. A group of extents recorded in an interleaved arrangement on a recording medium is used both in 3D video playback and 2D video image playback, as described below.
From among the extents recorded on the optical disc 9201; a 2D playback device 9204 causes an optical disc drive 9204A to read only the 2D/left-view extents 9202A-C sequentially from the start, skipping the reading of right-view extents 9203A-C. Furthermore, an image decoder 9204B sequentially decodes the extents read by the optical disc drive 9204A into a video frame 9206L. In this way, a display device 9207 only displays left-views, and viewers can watch normal 2D video images.
A 3D playback device 9205 causes an optical disc drive 9205A to alternately read 2D/left-view extents and right-view extents from the optical disc 9201. When expressed as codes, the extents are read in the order 9202A, 9203A, 9202B, 9203B, 9202C, and 9203C. Furthermore, from among the read extents, those belonging to the 2D/left-view video stream are supplied to a left video decoder 9205L, whereas those belonging to the right-view video stream are supplied to a right-video decoder 9205R. The video decoders 9205L and 9205R alternately decode each video stream into video frames 9206L and 9206R, respectively. As a result, left-views and right-views are alternately displayed on a display device 9208. In synchronization with the switching of the views by the display device 9208, shutter glasses 9209 cause the left and right lenses to become opaque alternately. Therefore, a viewer wearing the shutter glasses 9209 sees the views displayed by the display device 9208 as 3D video images.
When 3D video content is stored on any recording medium, not only on an optical disc, the above-described interleaved arrangement of extents is used. In this way, the recording medium can be used both for playback of 2D video images and 3D video images.